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full-auto breech :D

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Unread postAuthor: jackssmirkingrevenge » Fri Dec 14, 2007 8:24 pm

If your magazine tube was the same inner diameter as you ammunition and the mag was sealed off, this wouldn't be that much of a problem in practice. The Baikal Drozd's magazine works in the same manner.
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Last edited by jackssmirkingrevenge on Sat Dec 15, 2007 4:20 am, edited 1 time in total.
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Unread postAuthor: POLAND_SPUD » Fri Dec 14, 2007 8:41 pm

yes Flash I agree it would leak some air throught the magazine when fired.

however if the magazine tube is perfectly air tight air wouldn't leak out of the gun... the magazine tube volume ( minus the total volume of spring and ammo) can be treated in this design as deadspace....

if the ID of the magazine tube is as close to diameter of the ammo (spherical) as possible the amount of air that gets to the tube would be reduced to minimum....

I suppose performance would be only a bit lower than in jsr's desigin becasue an air powered bolt would always restrict the flow to some extend...

EDIT
JSR think how simple it is.... I think that all you would need to make the magazine is a 1/2" steel pipe for barrel & the magazine tube and a threaded steel t-fitting (like the one in the picture)... ah yes and an endcap for the magazine tube but that's obvious..... no machining no problem... :D
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Unread postAuthor: jackssmirkingrevenge » Sat Dec 15, 2007 12:37 am

I agree that a bolt does restrict flow, but the fact that it frees me from using a sealed spring loaded mag is a plus in my opinion. Of course it remains to be seen if I can get the bolt to cycle slowly enough to allow the next round to drop into the breech by gravity only.

I've been thinking about the design and perhaps it would be best to use a compression spring to return the bolt, as this configuration would be easier t otune - this would make it practically identical to the breech clide used in his GB semi, so much so that I can adapt his animation of the said launcher to illustrate what I had in mind:
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Unread postAuthor: VH_man » Sat Dec 15, 2007 7:47 am

Jack, why dont you use a spring-fed magazine???? it might give you the kind of ammo feed speed neccecary to keep up with your bolt..............
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Unread postAuthor: Hawkeye » Sat Dec 15, 2007 9:50 am

The trouble with just using a threaded T as a barrel/mag joining area is that the barrel and mag won't thread all the way in. There ends up being a considerable area where the ammo has space to rattle around. It doesn't just transition smoothly from one tube to the next.
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Unread postAuthor: jackssmirkingrevenge » Sat Dec 15, 2007 10:10 am

VH_man wrote:Jack, why dont you use a spring-fed magazine???? it might give you the kind of ammo feed speed neccecary to keep up with your bolt..............


I might have to do that but since the intnetion is to use it with soft lead pellets, I rather they were gravity fed from a hopper instead of being under pressure and deforming.

I'm making a second prototype as we speak, should be ready for primary testing by Monday latest. I doubt i'll get it right the first time but as long as it can be dismantled, i'm willing to put in the effort to try different spring strengths and lengths until it cycles reasonably. If that still doesn't work, the contingency plan is to attach the breech to a piston valve piloted by a homemade pressure relief valve.
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Unread postAuthor: POLAND_SPUD » Sat Dec 15, 2007 10:26 am

Hawkeye it is true with most t-fittings available today... but that is why I posted the picture of that t-fitting... a pipe can thread all the way in it.... I have dozens of them in sizes ranging from 1/2" to 2.5" in my basement :D

JSR do you cast pellets ? u could always use BBs or ball bearnings
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Unread postAuthor: jackssmirkingrevenge » Sun Dec 16, 2007 5:41 am

JSR do you cast pellets ? u could always use BBs or ball bearnings


I don't cast pellets, but I can buy them ;) remember, the idea here is to build something that has a lower rate of fire than a cloud/vortex BBMG, but has more power per shot. Since upping the pressure is not an option for sustained fire, I chose to go up in calibre. The only options I have for ammunition are airsoft BBs and airgun pellets, naturally since I'm looking for higher muzzle energy I'll go for the latter.

Damn this cold weather, if this was Summer the parts would be ready for testing by now :evil:

edit: here's some pics of the prototype while I wait for the epoxy to cure completely.

edit 2: Well, I've been testing the thing all afternoon and in spite of playing with spring strengths and addind lead weight to the bolt, still the same effect as before - either it cycles furiously sounding like an angry wasp, or it doesn't cycle at all.

In conclusion, I don't think any amount of tuning is going to make it work with a constant flow of air at compressor pressures. Next step is to see what sort of performance it gives with single shots, to see if it's worth making a "pulsed" air supply like this.
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bfv203.jpg
end view of the two sections, with the bolt and spring in the rear section
bfv202.jpg
rear section removed, with bolt held in "rest" position by spring
bfv201.jpg
Prototype in disassembled form, from left to right barrel section with ammunition feed slot and rubber damper in male thread, bolt section with cast epoxy stopper and rear section with brass tube air feed that also doubles as a bolt housing
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Unread postAuthor: jackssmirkingrevenge » Mon Dec 17, 2007 1:15 pm

here's the video, for more details read the edit above.

[youtube]http://www.youtube.com/watch?v=sawSgI5kOac[/youtube]

:?
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Unread postAuthor: VH_man » Mon Dec 17, 2007 6:23 pm

JSR, i seriously think you should make a spring-loaded magazine.........

it cant deform the pellets unless the spring is like uber strong...........
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Unread postAuthor: punkin » Mon Dec 17, 2007 8:20 pm

"Jack"...see my thread, I'm pissed, because this defies logic.

:? --Scott
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 18, 2007 3:14 am

VH_man wrote:JSR, i seriously think you should make a spring-loaded magazine.........

it cant deform the pellets unless the spring is like uber strong..........


The bolt is cycling so fast that it wouldn't make a difference anyway

I'm pissed, because this defies logic.


likewise :evil:

The next step for me is to hook up the breech to one of my mini-piston launchers and see what sort of power I get with single shots, if it's worthwhile I'll start on the pop-off piloted piston setup.
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Unread postAuthor: POLAND_SPUD » Tue Dec 18, 2007 1:45 pm

worth trying... A semiauto that works is better than fullauto that doesn't.... at least it is less frustrating....

What about adding more weight to the bolt, someone suggested you that AFAIK? have you tried that?

ps. yesterday I finally decided to ordered a QEV for Christmas to build a semi (either the spring loaded mag design or that design with a bolt and an aircylinder) but today I've recived an email that they would send me it in January..... so don't worry JSR life sucks for me too... :evil:
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 18, 2007 2:13 pm

POLAND_SPUD wrote:worth trying... A semiauto that works is better than fullauto that doesn't.... at least it is less frustrating....

What about adding more weight to the bolt, someone suggested you that AFAIK? have you tried that?


I tried it already, read the edited post:

edit 2: Well, I've been testing the thing all afternoon and in spite of playing with spring strengths and addind lead weight to the bolt, still the same effect as before - either it cycles furiously sounding like an angry wasp, or it doesn't cycle at all.


I just finished making my homemade adjustable pop-off valve :) I should have something workable by the end of this week, depending on how long it takes the epoxy to cure.
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Unread postAuthor: chrissilvermancs » Sat Mar 14, 2009 9:11 pm

i don't know if someone already mentioned this but i took some spare metal parts to test this concept and because i spent little to no time making it there wasn't a good seel and i used a bungee cord but i got to thinking

what about auto tennis ball gun same concept lager scale 2" pvc pits great in 2.5" pipe do u think it would work or do u guys know a better way of doing a auto system for bigger objects?
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